RIVER TURBINES Introduction

RIVER TURBINES
Introduction
The hydro-kinetic turbines are
designed to generate electricity
solely from the kinetic energy of
running water in a river or from
tidal currents when used in marine
settings. The conventional
technique of generating electricity
from hydrological energy is done
using water from a high position
that falls through a head onto a
turbine, where water is channelled
along canals and pipes in order to
make use of its potential energy.
This approach is covered in the
Practical Action technical brief on
micro hydro.
Figure 1: A river current turbine in Peru. Photo: Soluciones
The use of kinetic energy from
Prácticas.
river currents energy is a less
common, alternative approach to
hydro power where there is zero
head. The energy is converted into
electricity or used directly to power a mechanical water pump for irrigation.
Making use of kinetic energy of river currents was a traditional way to mill flour along with
wind power but was gradually replaced by fossil fuel systems. There is now renewed interest in
river current turbines in a wide range of countries for electricity generation. Practical Action
has been involved in promoting small-scale turbines to provide electricity to remote villages in
the Amazon and to supply water for irrigation in Sudan.
The power available from the river
Most of the principals of this type of turbine are based upon wind turbines, as they work in a
similar way. The power available (Pa ) in watts can be worked out using the following formula.
P a = ½ x C p x ρ x A x v3
A = area in metres squared (m2)
ρ = density of water (1000 kg/m3)
V = velocity of water (m/s)
Cp = the power coefficient = 16/27 = 0.592 (theoretical maximum power available)
The theoretical maximum power available from the river is expressed by the equation above
using a power coefficient of 0.592 or 59% efficiency. But a small-scale river turbine has its
own losses which will reduce the power coefficient to around 0.25.
The significant aspect to the equation is that the power increases in a cubed relationship to
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River turbines
Practical Action
the velocity of the flow of water past the turbine. Therefore it is important to find the best flow
to get the best power output.
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30
25
Power (kW)
Hydro-kinetic turbines can
be classified into two types.
The first is the vertical-axis
turbine, whose turning axis is
perpendicular to stream flow;
secondly, the axial turbine,
whose rotational axis follows
the direction of flow.
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15
10
Vertical-axis turbines are
preferable in situations
where flow direction
changes, such as in tidal
systems. These turbines are
designed so that the
direction of rotation remains
the same regardless of the
direction of flow.
5
0
0.25 0.5
0.75
1
1.25 1.5
1.75
2
2.25
2.5
2.75
3
3.25
3.5
3.75
Velocity (metres)
Figure 2: Graph showing the relationship between the speed of
the river and the power available. The green line shows the power
in the river. The red line shows the power extracted by the
turbine.
Putting the theory into practice
For small scale low cost river turbines Practical Action found the second configuration to work
due to the simplicity of the design and its greater robustness. It also has the advantage of
building on existing knowledge from the small scale wind turbine projects previously
undertaken.
The experience from Peru highlighted the importance of siting the turbine. The minimum
workable velocity of the river is about 0.8m/s to 1m/s but preferably 1.3 to 1.5 m/s going up
to a maximum of 3 m/s for the type of floating turbines Practical Action has been involved in.
The engineering would need to be more substantial for higher river speeds.
Larger rivers are better in providing the right conditions for a turbine but flow of a river can
vary considerably over the year. In a full river the turbine can be located near to the bank and
still work in deep water but during the dry season the water levels can drop and the turbine
could potentially hit the bottom.
If the bank has a shallow incline then the edge of the water moves away from its originally
position as the water level drops and the turbine needs to be moved further into the middle of
the river.
Therefore it is important to find a site that has a site where the water will have a fast flow near
to steep banking.
A major hazard for river turbines in large rivers is debris such as logs or trees that have fallen
into the river. These can seriously damage the turbine and incur large costs.
Banks can be eroded away or become unstable and in extreme cases the river can change its
course. These environmental issues can be more challenging than the technical issues.
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River turbines
Practical Action
The Design
The small-scale design designed by Practical
Action focuses on providing battery charging
facilities for remote communities. Typically, a
small turbine with a capacity of 200w could
charge 4 batteries in a day. The machine was
manufactured by the local company Tecnologia
Energética S.A.C. - Tepersac based in Lima, Peru.
turbine blades
The design of blades is achieved using concepts
used in wind turbine blade with the proviso that
in this case, the machine is subjected to much
stronger forces with, of course, a denser fluid
(water).
In order to calculate the diameter of the rotor,
following formula is applied:
P = ½ x ρ x (A) x v3 x Cp x h
A = (π x d2 / 4)
d = √ (8 x P/ π x p x V3 x Cp x h)
d : diameter of turbine rotor (m)
P : power of aero-generator design (Watts)
ρ : density of water (kg/m3)
V : velocity of river water (m/s)
A : area covered by the turbine (m2)
Cp : power coefficient (no dimensions)
h : efficiency of the generator
Figure 3: A robust and simple design was
developed for remote locations. A simple
permanent magnet generator was designed
(painted blue). Photo: Soluciones Prácticas.
λ = U/VD = π x N x d/60 x VD
N = (60 x λ x VD / π x d)
N : velocity of turbine rotor (r.p.m)
λ : tip speed ratio
U : tangential velocity at the tip of the blade (m/s)
Vp : design velocity (m/s)
The rotor
• Three fibre-glass blades
• Nominal diameter: 1.75m
• Turning speed: 45 rpm, at 1 m/s to the speed of river flow
• Two stainless steel supporting plates for the bucket mounting
The generator
In order to reduce costs, and to be able to rely on locally-made technology, Practical Action
began by working on the development of a permanent magnet generator. The magnets allowed
the speed of generation to be reduced, and lowered the cost of the equipment, which itself
could be adapted to be a river turbine rotor, and ultimately, tested and built. The main
components of the system are: the generation of alternating current which, via a system of
rectifying diodes, transforms the voltage to 12V, and 250W of power at 360 rpm.
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River turbines
Practical Action
Transmission shaft
A galvanised steel tube 1.5 inches in diameter, connected directly to the rotor. This tube is
layed inside a second, similar tube, 2.5 inches in diameter, which serves as protection and
support.
Other component parts
Fan belt
An intermediate component
connecting the transmission shaft
and the generator, it amplifies
velocity.
Control panel
This includes basic measuring
instruments and the aforementioned
12V rectifying diodes.
Floats
The floats can be made in a number
of ways based on what is most
suitable in terms of the materials
available. This could be a boat. In
Peru balsa wood float(s) were made
locally by inhabitants of the village
were used as this was the cheapest
option.
Figure 4: Setting up the fan belt and permanent magnet
generator . Photo: Soluciones Prácticas.
Further reading and bibliography
Saúl Ramírez; Rafael Escobar. 2002 Turbina de rio: una alternativa energética para la
Amazonía (River turbine: alternative energy in the Amazon). Hidrored 2/2002
Rudi Henri van Els; Clovis de Oliveira; Antonio Mantel Dias; Luís F. Balduino. 2003.
Turbina hidrocinética para poblaciones aisladas. (The hydro-kinetic turbine in isolated
communities.) Hidrored 1/2003
Diseño de una turbina de río para la generación de electricidad en el distrito de MazánRegión Loreto. Francisco Maldonado Quispe, Universidad Nacional Mayor de san Marcos,
2005.
Micro-Hydro Power Technical Brief Practical Action
Water Current Turbines P Garman Practical Action Publishing 1986
Pumps as Turbines A Williams Practical Action Publishing 2003
Micro-hydro Pelton Turbine Manual J Thake Practical Action Publishing 2000
Designing and Building Mini and Micro Hydro Power Schemes L Rodriguez & T Sanchez
Practical Action Publishing 2011
Micro-hydro Power Fraenkel et al Practical Action Publishing 1991
Motors as Generators for Micro-hydro Power N Smith Practical Action Publishing 2007
Micro Hydro Design Manual A Harvey Practical Action Publishing 1993
Contacts
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River turbines
Thropton Energy Services
Physic Lane, Thropton, Northumberland
NE65 7HU
United Kingdom
Tel: +44 1669 621288
Fax: +44 1669 621288
E-mail: enqs@throptonenergy.co.uk
Web: http://www.throptonenergy.co.uk/
Practical Action
Ampair
PO Box 416
Poole
Dorset
BH12 3LZ
United Kingdom
Tel: +44 (0)1202 749994
Fax +44 (0)1202 736653
E-mail: info@ampair.com
Website: http://www.ampair.com/
Underwater micro hydro 100w generator
This Technical Brief is based on the document
produced in Spanish by Giannina Solari,
Soluciones Prácticas and translated by Edward
Stevens for Practical Action. Additional
information was provided by Teo Sanchez.
info@solucionespracticas.org.pe
www.solucionespracticas.org.uk
Practical Action
The Schumacher Centre
Bourton-on-Dunsmore
Rugby, Warwickshire, CV23 9QZ
United Kingdom
Tel: +44 (0)1926 634400
Fax: +44 (0)1926 634401
E-mail: inforserv@practicalaction.org.uk
Website: http://practicalaction.org/practicalanswers/
Practical Action is a development charity with a difference. We know the simplest ideas can have the
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